feat(canvas): 交互可读性 - 优化连线、字号与工作条

web/src/lib/canvas/canvas-text-scale.ts

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+const DEFAULT_TEXT_NODE_WIDTH = 340;
+const DEFAULT_TEXT_NODE_HEIGHT = 240;
+const DEFAULT_TEXT_FONT_SIZE = 14;
+const MIN_TEXT_FONT_SIZE = 8;
+const MAX_TEXT_FONT_SIZE = 72;
+
+/**
+ * Keep text readable while a text node is resized.
+ *
+ * The geometric mean makes the scale respond to both dimensions without making
+ * a very wide, short node grow as aggressively as a purely width-based rule.
+ */
+export function canvasTextFontSize(width: number, height: number, baseFontSize = DEFAULT_TEXT_FONT_SIZE) {
+    const safeWidth = Number.isFinite(width) && width > 0 ? width : DEFAULT_TEXT_NODE_WIDTH;
+    const safeHeight = Number.isFinite(height) && height > 0 ? height : DEFAULT_TEXT_NODE_HEIGHT;
+    const safeBaseFontSize = Number.isFinite(baseFontSize) && baseFontSize > 0 ? baseFontSize : DEFAULT_TEXT_FONT_SIZE;
+    const scale = Math.sqrt((safeWidth / DEFAULT_TEXT_NODE_WIDTH) * (safeHeight / DEFAULT_TEXT_NODE_HEIGHT));
+    return Math.min(MAX_TEXT_FONT_SIZE, Math.max(MIN_TEXT_FONT_SIZE, safeBaseFontSize * scale));
+}